Slurry supply apparatus and method

ABSTRACT

A slurry supply apparatus includes a slurry supply tank, CMP unit, ultrasonic dispersion unit, and filter. In the slurry supply tank, a slurry obtained by dispersing abrasive grains with a predetermined grain size in a chemical solution is agitated and stored. The slurry is supplied from the slurry supply tank to the CMP unit through a slurry supply line. The ultrasonic dispersion unit pulverizes the abrasive grains formed by cohesion and supplied from the slurry supply tank through the slurry supply tank. The filter removes an abrasive grain with the predetermined grain size or less, which is supplied from the ultrasonic dispersion unit and supplies the resultant slurry to the CMP unit. A slurry supply method is also disclosed.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a slurry supply apparatus and a method therefor and, more particularly, to a slurry supply apparatus and method for supplying a slurry to a chemical mechanical polishing (CMP) unit.

[0002] In recent years, as the integration degree and performance of semiconductor integrated circuits increase, the CMP method is introduced as a micropatterning technique. The CMP method is a technique utilized often in planarization of an interlevel insulating film, metal plug formation, and buried interconnection formation in an LSI (Large Scale Integrated circuit) manufacturing process, particularly in a multilevel interconnection forming process. A CMP unit which polishes a semiconductor wafer manufactured by this technique is comprised of, e.g., a lower table to which a polishing cloth is adhered, and a vertically movable, pivotal and rotatable upper table for supporting the semiconductor wafer with a backing pad. To polish the semiconductor wafer, a slurry dispersed with abrasive grains with a predetermined grain size is supplied onto the polishing cloth of the lower table.

[0003] As the slurry used for polishing a metal, e.g., copper, used to form an interconnection, one having abrasive grains with a predetermined grain size and containing an oxidizing material as main components is generally employed. For example, such a slurry is formed by dispersing abrasive grains made of SiO₂, alumina, CeO₂, MnO₂, or Mn₂ 0 ₃ and with a grain size of about 0.01 μm to 1 μm in a chemical solution containing about 1 wt % to 10 wt % of an oxidant, e.g., hydrogen peroxide (H₂O₂), ferric sulfide (Fe(No₃)₃), or potassium periodate (KIO₃), a dispersant, or the like.

[0004] A semiconductor device is polished with such a slurry by mechanically removing the obtained oxide with abrasive grains while oxidizing the surface of a metal as a polishing target material by the oxidizing operation of an oxidizing material. Recent micropatterned semiconductor devices require polishing with a uniform surface roughness. The surface roughness is determined by the grain size of the abrasive grains. Thus, to increase the uniformity of the surface roughness, the classification precision of the abrasive grains themselves must be increased. In general, however, abrasive grains with a predetermined diameter or more are inevitably mixed in the slurry.

[0005] It is known that, when the grain size of the abrasive grains decreases, the interface energy of the surface of the single abrasive grain increases, and the abrasive grains attract each other to cause cohesion. To prevent this cohesion, surface treatment or dispersion promoting treatment may be performed. Yet, when a predetermined period of time has elapsed, cohesion occurs again. The large grains may form a large scratch on the polishing target surface or degrade the uniformity of the surface roughness. For example, when a scratch is formed on the surface of an insulating film, a polishing agent is left on the surface of the insulating film to cause heavy metal ion contamination, leading to an operation error of the semiconductor device. When a scratch is formed on the surface of a metal film, it causes a conduction error or degrades the electromigration resistance.

[0006] To remove large grains formed by cohesion of such abrasive grains, a method of building a filter having pores with a predetermined diameter in a slurry supply apparatus is known. A conventional slurry supply apparatus of this type will be described with reference to FIG. 3. As shown in FIG. 3, a conventional slurry supply apparatus 1 has a slurry supply tank 3 and slurry supply line 4. A filter 6 is installed midway along the slurry supply line 4 that connects the slurry supply tank 3 and a polishing unit such as a CMP unit 2.

[0007] In the slurry supply apparatus 1 with the above arrangement, the slurry supplied from the slurry supply tank 3 passes through the filter 6 to remove large grains in it, and is supplied to the turn table of the CMP unit 2. How the large grains are removed will be described with reference to FIGS. 4A and 4B.

[0008] Near the outlet of the slurry supply tank 3, abrasive grains Sa with a small grain size and large grains Sb formed by cohesion of the abrasive grains in the slurry discharged from the slurry supply tank 3 of the slurry supply apparatus 1 are distributed with respective peaks as shown in FIG. 4A. After passing through the filter 6, the large grains Sb formed by cohesion of the abrasive grains are removed, as shown in FIG. 4B, to leave only the abrasive grains Sa with the small grain size, and the slurry with the uniform abrasive grain size is introduced to the CMP unit 2.

[0009] In the conventional slurry supply apparatus 1 described above, although the large grains can be removed by the filter 6, the filter 6 tends to clog and thus has a short service life. For this reason, the filter 6 must be exchanged often, and accordingly the down time of the CMP unit 2 and the cost of filter components increase, leading to an increase in the cost of the semiconductor devices.

[0010] In order to reduce the load on the filter 6, the slurry in the slurry supply tank 3 is agitated so the abrasive grains are dispersed. It is, however, difficult to completely disperse the abrasive grains in the slurry supply tank 3. Even if the abrasive grains are dispersed, they cause cohesion again while the slurry passes through the slurry supply line 4. If the slurry is agitated strongly or for a long period of time in order to increase the dispersion properties, the viscosity of the slurry increase. In this case, the polishing performance itself degrades, e.g., the polishing speed decreases or the uniformity degrades, and the slurry supply amount fluctuates.

SUMMARY OF THE INVENTION

[0011] It is an object of the present invention to provide a slurry supply apparatus and method which do not apply a load on a filter installed midway along a slurry supply line.

[0012] It is another object of the present invention to provide a slurry supply apparatus and method which can effectively remove large grains formed by cohesion of abrasive grains from a slurry.

[0013] In order to achieve the above objects, according to the present invention, there is provided a slurry supply apparatus comprising a slurry supply tank in which a slurry obtained by dispersing abrasive grains with a predetermined grain size in a chemical solution is agitated and stored, a polishing unit to which the slurry is supplied from the slurry supply tank through a slurry supply line, ultrasonic dispersion means for pulverizing the abrasive grains formed by cohesion and supplied from the slurry supply tank through the slurry supply tank, and filter means for removing an abrasive grain with not less than a predetermined grain size, which is supplied from the ultrasonic dispersion means and supplying the resultant slurry to the polishing unit.

DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a view schematically showing the arrangement of a slurry supply apparatus according to an embodiment of the present invention;

[0015]FIGS. 2A, 2B, and 2C are graphs showing the distributions of abrasive grains contained in the slurry at points a, b, and c, respectively, of the slurry supply line shown in FIG. 1;

[0016]FIG. 3 is a view schematically showing the arrangement of a conventional slurry supply apparatus; and

[0017]FIGS. 4A and 4B are graphs showing the distributions of abrasive grains contained in the slurry at points a and b, respectively, of a conventional slurry supply line.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0018] The present invention will be described in detail with reference to the accompanying drawings.

[0019]FIG. 1 schematically shows the arrangement of a slurry supply apparatus according to an embodiment of the present invention. As shown in FIG. 1, a slurry supply apparatus 11 is comprised of a slurry supply tank 13, a polishing unit such as a CMP unit 12 connected to the slurry supply tank 13 through a slurry supply line 14, an ultrasonic dispersion unit 15 with an ultrasonic oscillator 15 a and disposed midway along the slurry supply line 14, and at least one filter 16 provided downstream of the ultrasonic dispersion unit 15.

[0020] In this arrangement, when the slurry supplied from the slurry supply tank 13 passes through the ultrasonic dispersion unit 15, most of large grains contained in the slurry are pulverized, and only those large grains which are not pulverized but left in a small amount are trapped by the filter 16.

[0021] The size of the abrasive grains contained in the slurry is usually from about 0.01 μm to 1 μm. SiO₂, alumina, CeO₂, MnO₂, Mn₂O₃, or the like can be used as the abrasive grains, and is dispersed in a chemical solution containing about 1 wt % to 10 wt % of a dispersant, oxidant, or the like. As the oxidant, hydrogen peroxide (H₂O₂), ferric sulfide (Fe(No₃)₃), potassium periodate (KIO₃), or the like is used.

[0022] How the large grains are removed from the slurry by the slurry supply apparatus 1 will be described with reference to FIGS. 2A, 2B, and 2C. In FIGS. 2A to 2C, the abscissa represents the abrasive grain size. The closer to the right side of the graph, the larger the abrasive grain size. The ordinate represents the strength, i.e., the number, of abrasive grains.

[0023] As shown in FIG. 2A, the slurry discharged from the slurry supply tank 13 has both the peak of abrasive grains Sa with a small grain size and the peak of large grains Sb formed by cohesion of the abrasive grains. The peak of the large grains Sb is considerably large. In other words, at this stage, a considerably large number of large grains are contained in the slurry.

[0024] When the slurry passes through the ultrasonic dispersion unit 15, the large grains Sb are pulverized by ultrasonic vibration of the ultrasonic oscillator 15a to improve the dispersion properties of the abrasive grains, as shown in FIG. 2B. Thus, the peak of the abrasive grains Sa with the small grain size becomes large, while the peak of the large grains Sb with the large grain size, which is formed by cohesion becomes small.

[0025] The ultrasonic oscillator 15 a need not be a particularly specific one, and suffices if it is, e.g., an oscillator that can generate ultrasonic waves in the range of 0.1 W/cm² to several 100 W/cm² at a frequency of 10 kHz to several GHz. As a method of applying the ultrasonic waves, the slurry may be temporarily put in a tank and ultrasonic waves may be applied to it. Alternatively, the pipe of the slurry supply line 14 may be clamped, and ultrasonic waves may be applied. The flow rate of the slurry is usually about 50 cc/min to 500 cc/min.

[0026] When the slurry in which the large grains with a large grain size have been pulverized by the ultrasonic dispersion unit 15 further passes through the filter 16, the large grains Sb with the large grain size are completely removed, as shown in FIG. 2C, and only the abrasive grains Sa with the small grain size are supplied to the turn table of the CMP unit 12.

[0027] The mesh size of the filter may be selected in accordance with the abrasive grain size. The present invention is not limited to a method that uses one filter matching the grain size of the abrasive grains to be passed. For example, a plurality of filters for removing abrasive grains, from those with a large grain size to those with a small grain size gradually, may be connected in a subordinate manner, so only abrasive grains with a desired grain size may be passed through the filters. When the plurality of filters are to be used, the abrasive grains with the large grain size are removed by a front filter, and the abrasive grains with the small grain size are removed by a rear filter. This can prolong the service life of the filters 16 more than in a case wherein one filter 16 is used.

[0028] In this manner, since the ultrasonic dispersion unit 15 and filter 16 are sequentially arranged from the upstream of the slurry supply line 14 that connects the slurry supply tank 13 and a polishing unit, e.g., the CMP unit 12, of the slurry supply apparatus 11, most of the large grains formed by cohesion of the abrasive grains with the small grain size can be pulverized by the ultrasonic dispersion unit 15. Since the large grains that are not pulverized but left can be completely removed by the filter 16 provided immediately before the CMP unit 12, a slurry containing only uniform-diameter abrasive grains with the small grain size can be supplied to the CMP unit 12. When compared to the conventional case wherein only the filter 6 is used, the load to the filter 16 can be reduced, so that the service life of the filter 16 can be greatly prolonged.

[0029] In the above embodiment, a case wherein the slurry is supplied to the CMP unit 12 is described. However, the present invention is not limited to this, and can also be applied to other polishing apparatus, cutting apparatus, pulverizing apparatus, or the like using a slurry dispersed with abrasive grains, as a matter of course.

[0030] As has been described above, according to the present invention, the serve life of the filter used for removing large grains is prolonged so that the cost of the filter can be reduced, and the down time of the apparatus necessary for exchanging the filters is shortened so that the time efficiency of the apparatus can increase. Thus, the manufacturing cost of the semiconductor devices can be reduced.

[0031] This is due to the following reason. Since ultrasonic waves are applied to the slurry by using the ultrasonic dispersion unit, the large grains formed by cohesion can be pulverized. This pulverizing is performed on a supply line close to the use point, so the dispersion performance of the slurry itself, which is to be actually supplied to the turn table, can always be maintained at a high level. Since one or more filters having predetermined mesh sizes are provided downstream of the ultrasonic dispersion unit, the large grains formed by cohesion can be completely removed from the slurry, and the number of large grains reaching the filters is reduced by the ultrasonic dispersion unit, thereby suppressing clogging of the filters. 

What is claimed is:
 1. A slurry supply apparatus comprising: a slurry supply tank in which a slurry obtained by dispersing abrasive grains with a predetermined grain size in a chemical solution is agitated and stored; a polishing unit to which the slurry is supplied from said slurry supply tank through a slurry supply line; ultrasonic dispersion means for pulverizing the abrasive grains formed by cohesion and supplied from said slurry supply tank through said slurry supply tank; and filter means for removing an abrasive grain with not less than the predetermined grain size, which is supplied from said ultrasonic dispersion means and supplying the resultant slurry to said polishing unit.
 2. An apparatus according to claim 1, wherein said ultrasonic dispersion means is clamped on a pipe of the slurry supply line, and adapted to apply ultrasonic vibration to the slurry through the pipe.
 3. An apparatus according to claim 1, wherein said polishing unit is a chemical mechanical polishing (CMP) unit.
 4. An apparatus according to claim 1, wherein said filter means is formed by connecting in a subordinate manner a plurality of filters that remove the abrasive grains from those with a large grain size to those with a small grain size gradually.
 5. An apparatus according to claim 1, wherein said ultrasonic dispersion means has an ultrasonic oscillator which generates ultrasonic waves in a range of 0.1 W/cm² to several 100 W/cm² at a frequency of 10 kHz to several GHz.
 6. A slurry supply method of supplying a slurry, obtained by dispersing abrasive grains with a predetermined grain size in a chemical solution and agitated and stored in a slurry supply tank, to a polishing unit through a slurry supply line, comprising the steps of: pulverizing the abrasive grains formed by cohesion and supplied from the slurry supply tank by using ultrasonic vibration; and removing an abrasive grain with not less than the predetermined grain size from the pulverized abrasive grains by using a filter, and thereafter supplying the slurry containing abrasive grains with less than the predetermined grain size to the polishing unit.
 7. A method according to claim 6, wherein the step of pulverizing comprises the steps of clamping an ultrasonic dispersion unit for applying ultrasonic vibration on a pipe of the slurry supply line, and applying ultrasonic vibration from the ultrasonic dispersion unit to the slurry through the pipe.
 8. A method according to claim 6, wherein the polishing unit is a chemical mechanical polishing (CMP) unit.
 9. A method according to claim 6, wherein the step of pulverizing has the step of generating ultrasonic vibration of ultrasonic waves in a range of 0.1 W/cm² to several 100 W/cm² at a frequency of 10 kHz to several GHz. 